A network may be formed between a femto cell base station inside a building and a Wibro base station outside of the building by connecting each other through a plurality of links. In this case, the femto cell base station and the Wibro base station should be temporally synchronized with each other. For example, where a user moves out of the building while making a phone call through the femto cell base station, the call is handed over to the Wibro base station, and the call quality may be substantially degraded if the time synchronization between the femto cell base station and the Wibro base station is not perfect. Hence, the femto cell base station needs to have the accurate time information synchronized with the Wibro base station.
To this end, the femto cell base station may include a global positioning system (GPS) receiver mounted thereon. However, since the femto cell base station is located inside the building, the GPS signals frequently fail to be received, and there may incur additional cost to mount the GPS receiver to the femto cell base station.
Alternatively, the femto cell base station may bring accurate time information from a different base station, for example, a master node, which has a GPS receiver. That is, the femto cell base station transmits a packet to a master node, and the master node receives the packet and returns the packet to the femto cell base station. The time spent for transmitting and returning the packet is called a round-trip delay, and a time difference between the femto cell base station and the master node is obtained by halving the round-trip delay. However, such a method may not be applied to an asymmetric network having a plurality of links with different uploading and downloading speeds, such as, but not limited to, an asymmetric digital subscriber line (ADSL) network.